Presumably vacman hasn't travelled by train in Cornwall much.
1. Saltash is a town with population over 15,000 (one of the largest towns in the County) and a rail catchment population of well over 50,000.
2. Smaller stops in Cornwall form a vital link for their communities - even Menheniot which is a mile from its village and gets about 3 trains a day in each direction is vital for both commuters and schoolchildren.
3. As everywhere an irregular service and lack of support form a viscous circle - the only way to break it is to provide services and publicise them - the passengers gradually start to come as they learn that the service is frequent, reliable, and cheap. Saltash is proving this works over the last year - passenger numbers well up.
4. The reason trains in Cornwall are relatively slow is to do with track and topography, not stops.

If you buy in to the DfT^» (Department for Transport - about) vision of a railway reduced to an inter-city mainline only service then you need to provide alternative transport options for users of local services on main lines.

The best use of the Cornish mainline would be to terminate all trains in both directions at Plymouth and so you could run a half-hourly clock face shuttle up and down the Cornish spine, linking properly with the branches, and not have our service continually crippled by constraints at Reading or Birmingham or service delays and problems elsewhere on the network.

Give Cornwall back its own railway - we could introduce passport and customs checks at the interchange at Plymouth as well 

RogerCO